Memory Wire

This nickel/titanium (NiTi) alloy initially ‘remembers’ that it should be straight. If it is bent into a different shape and then dropped in very hot water (90°C), it springs back to its original straight condition. It will repeat this behaviour any number of times.

The wire can also be heat treated to remember different shapes. It simply has to be held in the desired shape and then heated to 500°C in a small oven for a few minutes. This means that pupils can now get involved in creating smart springs and other components that a few years ago would have challenged front line researchers.

Memory wire has several important medical applications. It is used, for example, to make surgical stents – small woven frames that balloon outwards to open blocked arteries. It is also used for orthodontic braces. Some smart textiles use woven-in memory wire to change the shape (and support) of garments when they reach body temperature. Because it can be heat treated, the potential of memory wire in designing and making is virtually unlimited.

The wire is sold by the metre.

Two-Way Memory Spring

These remarkable springs, based on a brass alloy, ‘remember’ to open up at around 90°C and close again when cool. If immersed in hot water at or around 90°C they will open in a split second and close as quickly if dropped in cold water. Such springs have many industrial applications – e.g., in sprinkler and fire damping systems where they replace expensive single-use only fusible links. Memory springs open and close with considerable force and are used in countless applications where movement is wanted at the opening and closure threshold temperatures. Unusual applications include the heat engine pictured. As the springs open and close, they produce a continuous imbalance and cause the wheel to turn. Spring weight: 3 g.